Re: Understanding DateStyle guc in startup packet

On Fri, 2025-05-23 at 14:08 +0530, Manav Kumar wrote:
> Can you also share how does DRIVER comes to know the value been set for
> DateStyle is other than "ISO". and throw an error:
>  The server's DateStyle parameter was changed to Postgres, DMY. The JDBC driver requires DateStyle to begin with ISO
forcorrect operation.  
>
> I thought it used to read the PARAMETER STATUS packet that it receives
> from the server. But I tried changing it connection pooler i doens't
> see the same error. Can you point me to code where this assert check
> is present.  

See the method
org.postgresql.core.v3.QueryExecutorImpl.receiveParameterStatus()
https://github.com/pgjdbc/pgjdbc/blob/master/pgjdbc/src/main/java/org/postgresql/core/v3/QueryExecutorImpl.java#L2886

See the PostgreSQL documentation for context:
https://www.postgresql.org/docs/current/protocol-flow.html#PROTOCOL-ASYNC

  ParameterStatus messages will be generated whenever the active value
  changes for any of the parameters the backend believes the frontend
  should know about. Most commonly this occurs in response to a SET SQL
  command executed by the frontend, and this case is effectively
  synchronous — but it is also possible for parameter status changes
  to occur because the administrator changed a configuration file and
  then sent the SIGHUP signal to the server. Also, if a SET command is
  rolled back, an appropriate ParameterStatus message will be generated
  to report the current effective value.

Yours,
Laurenz Albe